怪怪 Origin — Dong Chinese Dictionary

guàiguài

odd/strange

guài strange

Phonosemantic compound. 忄 represents the meaning and 圣 represents the sound.

忄 Meaning component

xin, xīn heart

忄 is a component form of 心.

圣 Sound component

shèng sage, holy

Change in sound

怪 and 圣 don't sound similar in modern Mandarin due to historical phonetic changes. They were more similar in Old Chinese.
怪 *kruːds
圣 *kʰuːd

Regular Modern

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	Middle Chinese	Old Chinese	Gloss
Baxter-Sagart	kweajH	[k]ʷˤrə-s	extraordinary

《說文》：“怪，異也。从心，圣聲。”